Commonly known in the art are heat exchangers used in connection with an automotive vehicle for cooling the engine thereof. The heat exchanger generally comprises an upper and lower manifold providing fluid reservoirs and a plurality of coolant tubes extending between the manifolds and providing fluid communication therebetween. Coolant passes through the upper and lower manifolds. These type of heat exchangers are liquid to air because liquid passes through the tanks and tubes while air is passed external and between the tubes for cooling the fluid therein.
There are air to air heat exchangers wherein air is passed within the tubes and air is passed externally thereover for heat exchange. This type of exchanger may be used in turbo charged engines wherein heat exchangers are routinely used for cooling compressed "charged" air from a turbocharger, on route to the cylinders for combustion.
Heat exchangers often include fin structures disposed between coolant tubes for directing the ambient air about the coolant tubes. Such fins enhance heat exchange performance and are common in the art as shown in U.S. Pat. No. 4,821,795 to Lu, assigned to the assignee of the subject invention. Furthermore, fins have also been disposed within the fluid tubes of heat exchangers. See for example, U.S. Pat. No. 4,815,532 issued Mar. 28, 1989 in the name of Sasaki et al.
In heat exchangers, it has been known to vary the configuration of the fins located between the fluid tubes to enhance air heat exchange. See for example, U.S. Pat. No. 3,810,509, issued May 14, 1974 in the name of Kun and U.S. Pat. No. 4,815,532, issued Mar. 28, 1989 in the name of Sasaki et al.
It is also known that the fins may be comprised of a sheet material having a plurality of undulations and angled louvers cut therein. The sheet is slit and the resulting sections are angled with respect to the flat sheet to cause turbulence of air flow therein. However, a problem with these types of angled louvers is that they require high air flow power because of high air pressure drop. The angled fins create Eddy currents on the back side of the fins which results in stagnant air flow and pressure loss.
With straight and continuous fins, there is a build-up of stagnant boundary layers on the surface of the fin. The boundary layers start from zero at the edge of the fin and increase along the length of the fin until fully developed to be thick layers of insulation. Therefore, the air passing through the fins is flowing over the top of this stagnant boundary layer and heat flow between the fin and the air has to be conducted through this layer of insulation which minimizes heat exchange rate. It is desirable to brake up the fin into small sections to prevent the boundary layer growth to reduce the overall stagnant boundary layer thickness, therefore to minimize the average thickness of the stagnant layer of the fin. It is desirable to allow air to pass through the fin structure easily, but it is also necessary to maximize the air flow to provide maximum heat transfer while reducing air resistance and pressure loss. Furthermore, manufacturing consideration must be taken into account to allow simple manufacture of a complex design.